To evaluate reflex regulation of the circulation by determining the relative roles played by both arterial baroreceptors and cardiopulmonary receptors during specified physiological alterations. Both conscious dogs and anesthetized rabbits have been used. Also, additional evidence was obtained for the beat-to-beat regulation of heart rate and blood pressure by aortic nerve stimulation. Studies included the identification of the neural pathways regulating the cardiovascular response to acute volume loading and the evaluation of the interactions which may occur from reflexes arising from low and high pressure receptors. BIBLIOGRAPHIC REFERENCES: Stinnett, H.O., Peterson, D.F. and Bishop, V.S.: Cardiovascular responses to electrocardiogram-coupled stimulation of rabbit aortic nerve. Am. J. Physiol. 230:1374-1378, 1976. Bishop, V.S., Lombardi, F., Malliani, A., Pagani, M. and Recordati, G.: Reflex sympathetic tachycardia during intravenous infusions in chronic spinal cats. Am. J. Physiol. 230:25-29, 1976.